1. Field of the Invention
This invention relates to conductive polymeric materials comprising a resin-based structural material loaded with micron-sized conductive fibers providing conductive thermoplastic compositions. This invention also relates to antennas comprising this material.
2. Description of the Related Art
Antennas are essential parts of electronic communication systems that contain wireless links. Such applications as communications and navigation require reliable and sensitive antennas. Antennas conduct electrical signals and currents so that electromagnetic energy is transmitted and/or received. This requires that the materials of the antennas, especially the antenna elements, be electrically conductive, which in the past required that they be made from metals. Antennas have been typically fabricated from conductive metal antenna elements in a wide variety of configurations. Lowering the cost of antenna materials or production costs in fabrication of antennas offers significant advantages for any applications utilizing antennas.
Metals typically require high temperatures for fabrication into articles by molding techniques and/or their hardness makes machining articles more difficult, resulting in high fabrication costs. Metals may also be subject to corrosion or other environmental damage, particularly when placed in marine environments such as on boats or ships. Therefore, it is desirable to develop conductive materials other than metals from which to fabricate antennas. It is also desirable to reduce the weight of a wide variety of devices by the replacement of metal parts with lighter-weight components. Thermoplastic polymeric materials have often been used to replace metal parts because of their ease in fabrication and lower weight. However, typical thermoplastic polymers have been found to be nonconductive and therefore unsuitable for antenna applications. Thermoplastic polymers have been filled with conductive materials such as carbon black, conductive glass fibers, or metal powders or fibers to provide semiconductive compositions for use in applications such as electrostatic discharge and shielding wire, cable and electronic devices from electromagnetic interference (see for example, U.S. Pat. Nos. 4,169,816; 4,286,023; 5,004,561 and 6,409,942).
PCT Patent Application Publication WO 93/26013 describes a telescopic antenna comprising a principal structural component based on a polymeric material associated with or impregnated with conductive material in the form of fibers or particles. PCT Patent Application Publication WO 00/33418 describes a bar antenna comprised of an electrically conductive plastic. French Patent Application FR2660116 describes antennas comprising thermoplastic material impregnated with conducting material. U.S. Patent Application 20020109634 discloses antennas formed of conductive loaded resin-based materials.